Aqueous electrodeposition paints and the production and use thereof

ABSTRACT

Aqueous electrophoretic lacquer capable of being deposited cataphoretically, containing  
     A) an aqueous dispersion of cationically modified polyurethane (meth)acrylates (a1) with terminal, ethylenically unsaturated (meth)acrylic double bonds, and reactive thinner (a2) with at least two ethylenically unsaturated (meth)acrylic double bonds, the (meth)acrylic double bonds of the mixture of (a1) and (a2) corresponding to a bromine number of 20 to 150 g bromine/100 g solids, and  
     B) photoinitiators and optionally free-radical initiators capable of thermal activation,  
     the terminal, ethylenically unsaturated (meth)acrylic double bonds of the polyurethane (meth)acrylates being bonded with the anionically modified polyurethane prepolymer via urethane, urea, amide or ester groups,  
     and optionally conventional auxiliary substances and additives, pigments and/or fillers.

[0001] The invention relates to aqueous electrophoretic lacquers capableof being deposited cataphoretically, which are curable by high-energyradiation and have the advantage of a good full cure even with high filmthicknesses, and give good mechanical properties and, in particular,high resistance in an industrial gas atmosphere. It also relates totheir production and use for the lacquering of electrically conductivesubstrates, e.g. of metal, electrically conductive plastic, e.g.metallised plastic, or electrically conductive coatings.

[0002] Coatings applied by the electrophoretic lacquer process have theadvantage that they contain only a small quantity of residual water. Thecoating obtained does not therefore have to be pre-dried after rinsingoff any bath material still adhering, but can be cured by high-energyradiation after possibly blowing off droplets of water.

[0003] In U.S. Pat. No. 4,039,414, compositions for the electrophoreticlacquer process are described containing a photoinitiator, dispersed inan ethylenically unsaturated polymer, dispersed in an aqueous phase,which can be deposited at a cathode and cured with TV radiation. Ingeneral, a number of acrylated polymers are mentioned, among which, asthe only polyurethane acrylate, one that uses toluylene diisocyanate andpolyether polyols as structural components is described. Lacquers onthis basis have a tendency towards severe yellowing and towards earlysigns of degradation caused by weathering, leading to cracking,reduction in gloss and chalking, and also prove relatively brittle.

[0004] The invention was therefore based on the object of providingaqueous electrophoretic lacquers capable of being depositedcataphoretically, which do not exhibit these defects, which cure fullyby high-energy radiation, even in high film thicknesses, and givelacquer films with improved properties compared with the prior art,particularly with regard to resistance in an industrial gas atmosphere,improved flexibility and good adhesion to the substrate.

[0005] It has been shown that this object can be achieved with theaqueous electrophoretic lacquer capable of being depositedcataphoretically provided by the invention, which contains

[0006] A) an aqueous dispersion containing one or more cationicallymodified, preferably linear polyurethane (meth)acrylates (a1) withterminal, ethylenically unsaturated (meth)acrylic double bonds, and oneor more reactive thinners (a2) with at least two ethylenicallyunsaturated (meth)acrylic double bonds, the (meth)acrylic double bondsof the mixture of (a1) and (a2) corresponding to a bromine number of 20to 150 g bromine/100 g solids, and

[0007] B) optionally one or more photoinitiators and optionally one ormore free-radical initiators capable of thermal activation,

[0008] the terminal, ethylenically unsaturated (meth)acrylic doublebonds of the polyurethane (meth)acrylates being bonded with thecationically modified polyurethane prepolymer via urethane, urea, amideor ester groups,

[0009] and optionally conventional auxiliary substances and additives,pigments and/or fillers.

[0010] (Meth)acrylic here is intended to mean acrylic and/ormethacrylic.

[0011] As component (A), an aqueous, cationic polyurethane dispersionconsisting of e.g. 40 to 85 wt. % of component (a1), calculated as solidresin, and 15 to 60 wt. % of component (a2) is used. The aqueous,cationic polyurethane dispersion (A) has a solids content (polyurethane(meth)acrylate plus reactive thinner) e.g. of 30 to 70 wt. %, preferably40 to 55 wt. %. Its content of terminal, ethylenically unsaturated(meth)acrylic double bonds corresponds to a bromine number of 20 to 150,preferably 20 to 80 g bromine/100 g solids (polyurethane(meth)acrylateplus reactive thinner).

[0012] The aqueous dispersion (A) can be produced e.g. by the followingprocess:

[0013] A cationically modified urethane prepolymer with terminal NCOgroups is first produced by reacting

[0014] i) one or more aliphatic, cycloaliphatic, araliphatic and/oraromatic polyisocyanates, the aromatic polyisocyanates preferably havinga molecular weight of more than 174,

[0015] ii) one or more higher-molecular-weight polyhydroxyl compound(s)with a number average molecular weight (Mn) of e.g. 400 to 5000,preferably 1000 to 2500,

[0016] iii) one or more compound(s) having a group that is cationic byneutralisation and two groups that are reactive towards isocyanates and

[0017] iv) optionally one or more low-molecular-weight polyhydroxylcompounds, e.g. with a number average molecular weight (Mn) of 60 toless than 400.

[0018] The reaction can take place e.g. in a single- or multi-stepprocess, free from solvents or in a polar solvent inert towards NCOgroups.

[0019] The quantities of components (i) to (iv) in this process areselected e.g. such that the ratio of NCO groups to OH groups is between4:1 and 1.1:1.

[0020] The ethylenically unsaturated groups are then added to the freeNCO groups. This takes place e.g. by reacting with compounds (v), whichhave one or more ethylenically unsaturated (meth)acrylic groups and oneor more groups that are reactive towards isocyanates, the stoichiometricratios of groups that are reactive towards NCO groups to isocyanategroups being selected such that no free NCO groups remain.

[0021] To regulate the functionality (number of ethylenicallyunsaturated (meth)acrylic double bonds), compounds (vi) having one ormore, preferably one group that is reactive towards isocyanates, butcontaining no (meth)acrylic double bonds, can also be incorporated. Theycan contain other ethylenically unsaturated double bonds or can be freefrom them. Following the reaction of components (i) to (iv) for theproduction of a urethane prepolymer, the compounds (vi) can, forexample, be fed into the reaction before, together with or afterreaction with component (v).

[0022] The free NCO groups can, however, also be reacted first withcompounds which, in addition to a group that is reactive towardsisocyanates, contain one or more other reactive groups, which in turncan react with groups of ethylenically unsaturated (meth)acryliccompounds having complementary reactivity, such as e.g.hydroxycarboxylic acid with glycidyl (meth)acrylate. In this way, forexample, (meth)acrylic double bonds bonded to the polyurethaneprepolymer via ester groups can be introduced.

[0023] The cationically modified polyurethane (meth)acrylates withterminal, ethylenically unsaturated (meth)acrylic double bonds (a1) havea number average molecular weight Mn of e.g. 800 to 5000 and/or a weightaverage molecular weight Mw of 5000 to 20000, preferably less than20000. Their amine value is preferably 5 to 80, particularly preferably10 to 60. Their content of terminal, ethylenically unsaturated(meth)acrylic double bonds is preferably 4 to 80 g bromine/100 g solidresin, particularly preferably 5 to 35 g bromine/100 g solid resin.

[0024] The component (a1), obtainable as described above, is dilutedwith the reactive thinner (a2), at least partially neutralised andtransferred into the aqueous phase. At least 25% of the amino groups arepreferably present in neutralised form. The neutralising agent can beadded before or with the water, but it can also be previously added tothe water in which the polymer is dispersed. It is not necessary to addexternal emulsifiers. For the purpose of transferring into the aqueousphase, for example high-speed disc stirrers, rotor-stator mixers orhigh-pressure homogenisers are used. The inert solvent is then distilledoff, with the optional application of a vacuum.

[0025] However, the reactive thinner (a2) can also be added subsequentlyto the dispersion that is already aqueous. In this case the aqueousdispersion is produced as described above, with component (a1) initiallynot yet being diluted with the reactive thinner (a2) or only beingdiluted with part of the reactive thinner (a2).

[0026] Any organic di- and/or polyisocyanates with aliphatically,cycloaliphatically, araliphatically and/or aromatically bonded freeisocyanate groups having an average of more than one, preferably two,isocyanate groups per molecule are suitable as polyisocyanates (i).Aliphatically, cycloaliphatically and/or araliphatically bonded di-and/or polyisocyanates are preferred. Aromatic diisocyanates preferablyhave a molecular weight of more than 174.

[0027] Polyisocyanates containing about 3 to 36, particularly preferably8 to 15, carbon atoms are preferred. Examples of suitable diisocyanatesare diphenylmethane diisocyanate and particularly hexamethylenediisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate,dicyclohexylmethane diisocyanate, cyclohexane diisocyanate and mixturesthereof.

[0028] The so-called “polyisocyanate lacquer resins”, for example, basedon hexamethylene diisocyanate, isophorone diisocyanate and/ordicyclohexylmethane diisocyanate, are very highly suitable, i.e. thederivatives of these diisocyanates having biuret, urethane, uretdioneand/or isocyanurate groups, which are known per se.

[0029] Examples of suitable higher-molecular-weight polyhydroxylcompounds (ii) are linear or branched polyols, e.g. with an OH value of30 to 150. These are preferably saturated polyester and/or polyetherdiols and/or polycarbonate diols and/or so-called dimer fatty alcoholsand/or poly(meth)acrylate diols, each with a number-average molecularweight Mn of 400 to 5000, e.g. 500 to 5000, or mixtures thereof.

[0030] Suitable linear or branched polyether diols are e.g.poly(oxyethylene) glycols, poly(oxypropylene) glycols and/orpoly(oxybutylene) glycols, such as e.g. Terathane® grades from DuPont.

[0031] Polyester diols are preferred and can be produced in a knownmanner by esterification of dicarboxylic acids or their anhydrides withdiols. To produce branched polyesters, polyols or polycarboxylic acidswith higher functionality can also be used to a small degree.

[0032] Compounds containing two groups reacting with isocyanate, e.g.H-active groups, and at least one group capable of cation formation areintroduced as suitable compounds (iii). Suitable groups reacting withisocyanate groups are particularly hydroxyl groups. Groups capable ofcation formation are e.g. amino groups. Examples of these compounds arealkyl- or dialkylamino dialcohols with e.g. 1 to 8 C atoms in the alkylportion, the dialcohols optionally being aliphatic, cycloaliphatic oraromatic, aliphatic dialcohols having e.g. 2 to 18 and cycloaliphatice.g. 5 to 14 C atoms, or triamines with a tert. amino group, such ase.g. diethylaminopropanediol, methyldiethanolamine,N,N-diethylaminomethylamine, or ketimine-blocked triamines, such as e.g.ketimine-blocked diethylenetriamine. Aminotriols, such as e.g.triethanolamine, can optionally also be used.

[0033] Examples of suitable low-molecular-weight polyhydroxyl compounds(iv) preferably have a number-average molecular weight Mn of 60 to lessthan 500, e.g. of 60 to less than 400 and can contain aliphatic,alicyclic and/or aromatic groups. Suitable low-molecular-weightpolyhydroxyl compounds are e.g. diois, triols or polyols, such asethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol,1,3-propanediol, 1,4-butanediol, 1,2-butylene glycol, 1,6-hexanediol,trimethylolpropane, castor oil or hydrogenated castor oil,pentaerythritol, 2-cyclohexanediol, 1,4-cyclohexanedimethanol, bisphenolA, bisphenol F, neopentyl glycol, neopentyl glycol hydroxypivalate,hydroxyethylated bisphenol A, hydrogenated bisphenol A and mixtures ofthese polyols.

[0034] Suitable compounds (v) having one or more ethylenicallyunsaturated (meth)acrylic groups and one or more groups that arereactive towards isocyanates contain hydroxyl, amino and/or amide groupsas reactive groups. (Meth)acrylic double bonds bonded via urethanegroups are introduced into the polyurethane prepolymer via thehydroxyl-group-containing compounds (v); compounds (v) containing aminogroups lead to bonding via urea groups; compounds (v) containing amidegroups lead to bonding via “amide groups”, with α-ketourea groupsparticularly being formed.

[0035] Examples of hydroxyl-group-containing compounds (v) are hydroxy(meth)acrylates, such as e.g. hydroxyl-group-containing esters ofacrylic acid and/or methacrylic acid with 2 to 12, preferably 2 to 6 Catoms in the hydroxyalkyl radical, such as e.g. 2-hydroxyethyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl(meth)acrylate, 5-hydroxypentyl (meth)acrylate, 6-hydroxyhexyl(meth)acrylate, 7-hydroxyheptyl (meth)acrylate, 8-hydroxyoctyl(meth)acrylate and the corresponding isomeric compounds2-hydroxy-1-methylethyl (meth)acrylate, 1,3-dimethyl-3-hydroxybutyl(meth)acrylate and others; reaction products of (meth)acrylic acid withpolyols, such as eg. glycerol diacrylate, trimethylolpropane diacrylate,pentaerydritol triacrylate; pre-adducts of glycidyl nethacrylate andhydroxycarboxylic acids, such as e.g. glycolic acid; reaction productsof hydroxy (meth)acrylates with ε-caprolactone; reaction products of(meth)acrylic acid with the glycidyl ester of a carboxylic acid having atertiary α-C atom, such as e.g. Cardura® from Shell.

[0036] Examples of amino-group-containing compounds are amino(meth)acrylates, such as e.g. tert.-butylaminoethyl (meth)acrylate,(meth)acrylic acid-β-ureidoethyl ester or reaction products of(meth)acrylic acid chloride and diamines.

[0037] Examples of compounds with amide groups are (meth)acrylamide,N-methylol (meth)acrylamide and isobutylmethylol (meth)acrylamide. Thecompounds (v) can be used individually or as mixtures.

[0038] Suitable compounds (vi) for regulating the functionality are e.g.higher glycol ethers and/or fatty alcohols and/or fatty amines. One ormore aliphatic C₄-C₃₆ alcohols and/or amines can be used, for example,which are generally then reacted with complete consumption of their OH,NH or NH₂ groups. Fatty amines and/or fatty alcohols with more than 12 Cgroups are preferred. Examples are lauryl alcohol, stearyl alcohol andthe corresponding amines.

[0039] Ethylenically unsaturated, particularly low-molecular-weight andoligomolecular compounds, are suitable as reactive thinners (a2). Unlikethe polyurethane (meth)acrylate component (a1), the reactive thinners donot usually have any cationic modifications. The low-molecular-weightand/or oligomolecular reactive thinners can, for example, havecalculated molecular weights in the order of magnitude of up to 10000,e.g. 100 to 10000. Suitable reactive thinners are e.g. di- andpoly(meth)acrylates of glycols with 2 to 6 C atoms and polyols with 3 to4 OH groups and 3 to 6 C atoms, such as ethylene glycol diacrylate,1,3-propanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanedioldiacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate,pentaerythritol tetraacrylate and corresponding methacrylates, and alsodi(meth)acrylates of polyether glycols of glycol, 1,3-propanediol,1,4-butanediol, tetraefhoixylated trirmethylolpropane triacrylate and/oroligourethane (meth)acrylates with 2 to 6 ethylenically unsaturateddouble bonds. Mixtures can also be used.

[0040] Conventional inorganic acids are suitable as neutralising agents,such as e.g. hydrochloric acid, sulfuric acid, sulfurous acid,phosphoric acid and chromic acid, but organic acids are preferred,particularly monocarboxylic acids, such as e.g. formic acid, aceticacid, propionic acid and particularly hydroxycarboxylic acids, such ase.g. lactic acid, glycolic acid, diglycolic acid, malic acid, citricacid, mandelic acid, tartaric acid, hydroxypropionic acid anddimethylolpropionic acid. Mixtures of such neutralising agents can alsobe used.

[0041] The stability of the dispersion can be influenced in the way thatis familiar to the person skilled in the art by the selection of theneutralising agent. The quantity of neutralising agent is generallyselected such that at least 25% of the ionic groups are present in saltform.

[0042] The electrophoretic lacquers according to the invention canoptionally contain one or more photoinitiators and/or optionally one ormore free-radical initiators capable of thermal activation. Theelectrophoretic lacquers according to the invention are preferably curedin the presence of photoinitiators, but the curing can also take placewithout photoinitiators.

[0043] Any initiators that are conventional for free-radically curingsystems can be used as suitable photoinitiators (B), e.g. thoseabsorbing in the wavelength range of 190 to 600 nm.

[0044] Examples are acetophenone and derivatives, benzophenone andderivatives, benzil, Michler's ketone, thioxanthone and derivatives,anthrone, anthraquinone and derivatives; benzoin and derivatives,benzoin ether and derivatives, dialkoxy acetophenones, acyloxime esters,benzil ketals, hydroxyalkylphenones; organophosphorus compounds, such ase.g. acylphosphine oxides; haloketones. The photoinitiators are used inconventional quantities, e.g. of 0.1 to 20 wt. %, preferably 0.1 to 5wt. %, based on the sum of polymers that can be polymerised by freeradicals (a1) and reactive thinner (a2). The photoinitiators can be usedindividually or in combination.

[0045] In addition to the photoinitiators mentioned, so-calledphotoactivators, such as e.g. tertiary amines, can be added. Synergisticeffects are sometimes achieved with combinations of this type.

[0046] In a less preferred embodiment, the curing is performed withoutphotoinitiators.

[0047] The aqueous electrophoretic lacquer capable of being depositedcataphoretically according to the invention can contain conventionallacquer auxiliary substances and additives in addition to the aqueousdispersion (A) and the photoinitiator (B), such as e.g. biocides, lightstabilisers, flow promoters and optionally pigments and/or fillers.

[0048] The pigments and fillers in this case are the conventionalfillers that can be used in the lacquer industry and inorganic ororganic colouring and/or special-effect pigments and anticorrosivepigments. Examples of inorganic and organic colouring pigments aretitanium dioxide, micronised titanium dioxide, zinc sulfide, lithopone,lead carbonate, lead sulfate, tin oxide, antimony oxide, iron oxides,chrome yellow, nickel titanium yellow, chrome orange, molybdenum red,mineral violet, ultramarine violet, ultramarine blue, cobalt blue,chrome oxide green, carbon black, azo, phthalocyanine, quinacridone,perylene, perinone, anthraquinone, thioindigo and diketopyrrolopyrrolepigments. Examples of special-effect pigments are metallic pigments,e.g. of aluminium, copper or other metals; interference pigments, suchas e.g. metal oxide-coated metallic pigments or metal oxide-coated mica;pearlescent pigments and optically variable pigments (OVP).

[0049] Examples of fillers are calcium carbonate, barium sulfate,talcum, silicon dioxide, aluminium silicates, magnesium silicates, mica,aluminium hydroxide and silicas. The fillers can also be modified(coated) with organic compounds, which can also contain UV-curablegroups. Examples of these modified fillers are coated micronisedaluminium oxide or coated micronised silicon dioxide.

[0050] The aqueous electrophoretic lacquer capable of being depositedcataphoretically according to the invention can also contain otherhydrophilic and/or hydrophobic polymers with or without reactive groups,such as e.g. hydroxyl, amino and other groups or mixtures of thesepolymers, which can optionally also be thermally crosslinked.

[0051] Examples of these polymers are saturated or unsaturated acrylicor polyester resins, acrylate-modified acrylic or polyester resins,epoxy resins, aminoplastic resins, phenolic resins and blockedpolyisocyanates.

[0052] The electrophoretic lacquer is produced by mixing components (A)and (B) and optionally other lacquer auxiliary substances and additives,e.g. with the aid of conventional mixers such as e.g. (high-speed)stirrers, static mixers, rotor/stator mixers and other homogenisers.

[0053] The pigments and/or fillers that are optionally incorporated areprocessed in a portion of component (A) or a special paste resin in aknown manner by conventional dispersing processes to form a pigmentpaste, which is mixed into components (A) and (B) as described above.

[0054] In the case of the initial filling of an electrophoretic lacquerbath, the electrophoretic lacquer produced in this way can optionally beadjusted to the desired bath MEQ value with farther neutralising agentand adjusted to the desired bath solids with deionised water. The MEQvalue is a measure of the content of neutralising agent in a water-basedlacquer. It is defined as the quantity of milliequivalents of theneutralising agent based on 100 g of solids.

[0055] In the case of post-compensation, the amino groups of component(A) can be only partly neutralised to compensate for the neutralisingagent released during deposition.

[0056] The bath MEQ value is e.g. 15 to 70, preferably 20 to 45milliequivalents of neutralising agent, e.g. acid/100 g solids, and thebath solids content is 5 to 25%, preferably 8 to 18%.

[0057] The electrophoretic lacquer according to the invention issuitable for coating workpieces with an electrically conductive surface,e.g. metal, electrically conductive (e.g. metallised) plastic,electrically conductive wood or electrically conductive coatings (e.g.lacquers), for example for the priming and/or one-coat lacquering ofdomestic and electrical appliances, steel furniture, structuralcomponents and agricultural machinery and car accessories as well as carbodies, particularly for the clear lacquer coating of aluminium, such ase.g. of pretreated aluminium profiles, and for the sealing of conductivecoatings (e.g. electrophoretic lacquer coatings).

[0058] The coatings produced with the electrophoretic lacquer accordingto the invention can, however, also be provided with other lacquercoatings in the conventional way to form a multi-coat construction.

[0059] In a suitable coating plant, the substrate to be coated isimmersed in the electrophoretic lacquer bath filled with theelectrophoretic lacquer according to the invention and is connected asthe cathode in a DC circuit opposite a counter-electrode. These coatingplants are known to the person skilled in the art and described e.g. in“Glasurithandbuch” 1984, pages 374 to 384.

[0060] A film of up to film thicknesses of 60 μm, preferably between 10and 50 μm, is deposited, e.g. at a coating temperature of 15 to 30° C.,preferably 18 to 22° C. with a DC voltage of 50 to 500 volts, preferably100 to 300 volts for a coating period of 1 to 5 minutes, preferably 2 to3 minutes.

[0061] The deposition can take place both intermittently andcontinuously.

[0062] The deposited film is freed from any adhering bath material byrinsing with ultrafiltrate and/or deionised water, and freed from anydroplets of water that are clinging on by blowing off in an optionallyheated air stream or by supported evaporation with an IR radiator, andexposed to high-energy radiation, such as electron beam radiation,preferably UV radiation, for the purpose of curing.

[0063] For the radiation curing of the coating compound according to theinvention, any known sources of radiation can be used. Ad radiationsources, for example, with emissions in the wavelength range of 180 to420 nm, particularly 200 to 400 nm, are suitable. Examples of these UVradiation sources are high-pressure, medium-pressure and low-pressuremercury vapour radiators, gas discharge tubes such as e.g. xenon vapour,xenon/mercury vapour, (low-pressure) germanium vapour lamps, UVlight-emitting diodes and UV light-emitting lasers. The irradiation canalso take place with pulsed radiation, e.g. with pulsed UV radiation.So-called high-energy electron flash generators (UV flash lamps), asdescribed e.g. in WO-A-94 11 123 or EP-A-525 340 and commerciallyavailable, are particularly preferably used as sources of radiation.

[0064] The irradiation period is in the range of e.g. 1 millisecond to30 minutes, depending on the lacquer system and source of radiation. Thedistance from the source of radiation to the substrate surface to beirradiated is e.g. 2 to 50 cm, preferably 5 to 10 cm. The irradiationperiod is selected such that, as far as possible, a complete cure isachieved, i.e. the formation of the required technological properties isguaranteed. For this purpose, the substrate surface to be irradiated canbe passed in front of the source of radiation several times, or, withthe preferred use of UV flash lamps, the irradiation can take place witha multiple flash discharge. The flashes can be triggered e.g. every 4seconds, since the UV flash lamps do not require any bum-in period.

[0065] To avoid any radiation leakage, the sources of radiation areshielded against the environment.

[0066] In addition, it is possible to apply thermal activation tocrosslink the coating compounds according to the invention, in order tocure areas that can only be exposed to the radiation inadequately.

[0067] For this purpose it can be advantageous to incorporateconventional free-radical initiators that are capable of thermalactivation, so that, after the irradiation or at the same time as theirradiation, a thermally activated free-radical polymerisation takesplace.

[0068] Examples of free-radical initiators that are capable of thermalactivation are organic peroxides, organic azo compounds or C-C-splittinginitiators, such as e.g. dialkyl peroxides, peroxocarboxylic acids,peroxide carbonates, peroxide esters, hydroperoxides, ketone peroxides,azodinitriles or benzopinacole silyl ethers.

[0069] The free-radical initiators that are capable of thermalactivation can also be used in a mixture. The preferred amounts are 0.1to 5 wt. %, based on the sum of components (a1) and (a2), which can bepolymerised by free radicals.

[0070] The films deposited with the aqueous electrophoretic lacqueraccording to the invention and cured are distinguished by high gloss,very good adhesion and good edge coverage. In addition to high scratchresistance, they exhibit excellent resistance to acids, alkalis andsolvents and to industrial atmospheres, particularly acidic waste gases,such as sulfur dioxide, particularly in a damp atmosphere, which can beproved e.g. by the Kestemich test (DIN or ISO 3231).

[0071] Other advantages are a fully automatic process, high applicationefficiency, low-waste implementation as a result of closed circuits,low-solvent or solvent-free operation, extremely short curing times andlow thermal stress to the substrates to be lacquered.

EXAMPLE 1

[0072] 400.2 g of acetone, 133.0 g of diethylaminopropanediol and 849.8g of a polyester diol consisting of neopentyl glycol, adipic acid andisophthalic acid (OH value=106 mg KOH/g solid resin) are initiallyplaced in a reaction vessel with a stirrer, thermometer and refluxcondenser and reacted with 510.4 g of isophorone diisocyanate at 60° C.,until an NCO content of 1.7% is reached.

[0073] 106.6 g of hydroxyethyl acrylate are added to the NCO prepolymersolution thus obtained and stirred at 60° C. until the NCO content hasfallen below 0.2%.

[0074] 551.0 g of the polyurethane acrylate thus obtained are dilutedwith 188.9 g of trimethylolpropane triacrylate, neutralised with 58.7 gof 50% formic acid and, after stirring for 1 hour at 60° C., dispersedin 1194.6 g of deionised water. The acetone is removed by vacuumdistillation.

[0075] The dispersion thus obtained has a solids content (30 minutes150° C.) of 35% and a content of double bonds of 63 g bromine/100 gsolids.

[0076] 9.0 parts by weight of 2-hydroxy-2-methyl-1-phenylpropanone aredispersed in 857.1 parts by weight of the dispersion. This is thendiluted with 1133.9 parts by weight of deionised water.

[0077] In the electrophoretic lacquer bath thus obtained, zincphosphated steel plates are coated at a bath temperature of 25° C. for 2minutes with a series resistor of 200 ohms with 100 to 200 volts.

[0078] The deposited film is rinsed with water and freed from any waterdroplets that are clinging on by blowing off with compressed air. It isthen cured on a belt conveyor with 2 UV radiators (80 W/cm) at a beltspeed of 3×3 m. The cured films have a film thickness of 15 to 30 μm,are high-gloss and display very good flow.

[0079] Various tests were performed on the cured films with a 20 μm filmthickness; the results for Erichsen indentation, crosshatch adhesiontest and chemical resistance are listed below. Erichsen indentationaccording to EN-ISO 1520: 9-10 mm Crosshatch according to EN-ISO 2409:no detachment

[0080] Chemical resistance of vehicle lacquers based on VDA testspecification 621-412:

[0081] 10 minutes xylene no swelling or detachment

[0082] 60 seconds acetone no swelling or detachment.

1. Aqueous electrophoretic lacquer capable of being depositedcataphoretically, containing A) an aqueous dispersion containing one ormore cationically modified polyurethane (meth)acrylates (a1) withterminal, ethylenically unsaturated (meth)acrylic double bonds, and oneor more reactive thinners (a2) with at least two ethylenicallyunsaturated (meth)acrylic double bonds, the (meth)acrylic double bondsof the mixture of (a1) and (a2) corresponding to a bromine number of 20to 150 g bromine/100 g solids, and B) optionally one or morephotoinitiators and optionally one or more free-radical initiatorscapable of thermal activation, the terminal, ethylenically unsaturated(meth)acrylic double bonds of the polyurethane (meth)acrylates beingbonded with the anionically modified polyurethane prepolymer viaurethane, urea, amide or ester groups, and optionally conventionalauxiliary substances and additives, pigments and/or fillers. 2.Electrophoretic lacquer according to claim 1, characterised in that thebromine number of component (a1) is 4 to 80 g bromine/100 g solid resin.3. Electrophoretic lacquer according to claim 1 or 2, characterised inthat the aqueous polyurethane dispersion contains 40 to 85 wt. % ofcomponent a1) and 15 to 60 wt. % of component a2), based in each case onthe solids content of component A), and the solids content is 30 to 70wt. %.
 4. Electrophoretic lacquer according to one of claims 1, 2 or 3,characterised in that the dispersion A) is obtainable by preparing thepolyurethane (meth)acrylate (a1), by producing a urethane prepolymerwith terminal NCO groups, by reacting: i) one or more aliphatic,eycloaliphatic, araliphatic and/or aromatic polyisocyanates, aromaticpolyisocyanates having a molecular weight of more than 174, ii) one ormore polyhydroxyl compounds with a number average molecular weight Mn of400 to 5000, iii) one or more compounds having a group that is cationicby neutralisation and two groups that are functional towardsisocyanates, iv) optionally one or more polyhydroxyl compounds with anumber average molecular weight Mn of 60 to less than 400, andsubsequent reaction of the urethane prepolymer thus obtained (v) withone or more compounds which have one or more ethylenically unsaturated(meth)acrylic groups and one or more groups that are reactive towardsisocyanates, selected from hydroxyalkyl (meth)acrylates, aminoalkyl(meth)acrylates and/or (meth)acrylamides and/or with one or morecompounds having one group that is reactive with isocyanate and onegroup that is suitable for introducing a (meth)acrylic ester group, andsubsequent reaction for the introduction of a (meth)acrylic ester group,(vi) and optionally with one or more compounds with one or more groupsthat are reactive towards isocyanate, having no (meth)acrylic doublebonds, after which dilution is performed with the reactive thinner a2)and the mixture is transferred into the aqueous phase with at leastpartial neutralisation.
 5. Process for the production of an aqueousdispersion A) suitable for electrophoretic lacquers according to one ofclaims 1 to 4, characterised in that a urethane prepolymer with terminalNCO groups is produced by reacting: i) one or more aliphatic,cycloaliphatic, araliphatic and/or aromatic polyisocyanates, aromaticpolyisocyanates having a molecular weight of more than 174, ii) one ormore polyhydroxyl compounds with a number average molecular weight Mn of400 to 5000, iii) one or more compounds having a group that is cationicby neutralisation and two groups that are functional towardsisocyanates, iv) optionally one or more polyhydroxyl compounds with anumber average molecular weight Mn of 60 to less than 400, and theurethane prepolymer thus obtained is then reacted (v) with one or morecompounds which have one or more ethylenically unsaturated (meth)acrylicgroups and one group that is reactive towards isocyanate, selected fromhydroxyalkyl (meth)acrylates, aminoalkyl (meth)acrylates and/or(meth)acrylamides, and/or with one or more compounds having one groupthat is reactive with isocyanate and one group that is suitable forintroducing a (meth)acrylic ester group, and subsequent reaction for theintroduction of a (meth)acrylic ester group, (vi) and optionally withone or more compounds with one or more groups that are reactive towardsisocyanate, having no (meth)acrylic double bonds, after which dilutionis performed with the reactive thinner a2) and the mixture istransferred into the aqueous phase with at least partial neutralisation.6. Process for the electrophoretic lacquering of electrically conductivesubstrates by immersing in an aqueous electrophoretic lacquer,connecting the substrate as cathode and curing the deposited film,characterised in that an electrophoretic lacquer according to one ofclaims 1 to 4 is used and the curing is performed by means ofhigh-energy radiation.
 7. Process according to claim 6, characterised inthat thermal curing is additionally performed.
 8. Lacquered substrateobtained by the process of claim 6 or
 7. 9. Use of the electrophoreticlacquers according to one of claims 1 to 4 for the electrophoreticlacquering of electrically conductive substrates.
 10. Use of theelectrophoretic lacquers according to one of claims 1 to 4 for theproduction of multi-coat finishes.